In International Patent Specifications WO 95/08055 and WO 01/71160, the to contents of which are incorporated herein by reference, there are described internal combustion engines which utilise a pivoted piston which rocks about a pivot point within a combustion chamber. The piston is connected adjacent the end of the piston remote from the pivot point to a connecting rod which drives a crankshaft. The piston has a first arcuate sealing surface to seal against a wall of the combustion chamber and a second sealing surface which is connected by a piston floor to the first arcuate sealing surface. Both sealing surfaces have a substantially constant radial dimension from the pivot point of the piston.
The first arcuate sealing surface forms a skirt so a portion of the wall of the arcuate sealing surface will make a gas seal with the wall of the combustion chamber. The skirt also assists in dissipating heat in the piston. The piston further includes an arrangement to allow liquid coolant to pass through the pivot shaft, through liquid cooling galleries in the piston and out of the pivot shaft.
A particular area of difficulty with prior art two stroke engine configurations, both of the type noted above, but also more conventional designs which utilise a piston which reciprocates up and down within a circular cylinder bore, is in maximising pre-combustion cycle pressurisation of the combustion charge.